Hi, Catherine. This is pretty hard to answer without seeing your basement or a drawing, but I will give you a guess. Pick up some 6 mil or heavier plastic sheeting as wide as you can get it. Tape it to whatever butts up to the rock with aluminum duct tape to keep the plastic in place and seal the edges as much as possible. Don't bother trying to tape it directly to the rock, it probably will not hold.
Now go outside during a rain. Do your downspouts direct the water at least a meter and preferably 2 meters from the house? Does your ground slope away from the house for this distance? Keeping the water away from your house as much as possible is as important as sealing the rock face. But don't raise the ground level any closer than 1/3rd meter from any of the wood on your house and the further away, the better.